#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

int main(int argc, char** argv){
ros::init(argc, argv, "odometry_publisher");

ros::NodeHandle n;
ros::Publisher odom_pub = n.advertise<nav_msgs::Odometry>("odom", 50);
 tf::TransformBroadcaster odom_broadcaster;

 double x = 0.0;
  double y = 0.0;
 double th = 0.0;

 double vx = 0.1;
 double vy = -0.1;
  double vth = 0.1;

 ros::Time current_time, last_time;
 current_time = ros::Time::now();
 last_time = ros::Time::now();

ros::Rate r(1.0);
while(n.ok()){

  ros::spinOnce();               // check for incoming messages
   current_time = ros::Time::now();

  //compute odometry in a typical way given the velocities of the robot
   double dt = (current_time - last_time).toSec();
   double delta_x = (vx * cos(th) - vy * sin(th)) * dt;
   double delta_y = (vx * sin(th) + vy * cos(th)) * dt;
  double delta_th = vth * dt;

    x += delta_x;
   y += delta_y;
   th += delta_th;

  //since all odometry is 6DOF we'll need a quaternion created from yaw
   geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(th);

  //first, we'll publish the transform over tf
   geometry_msgs::TransformStamped odom_trans;
    odom_trans.header.stamp = current_time;
   odom_trans.header.frame_id = "odom";
    odom_trans.child_frame_id = "base_link";

  odom_trans.transform.translation.x = x;
   odom_trans.transform.translation.y = y;
  odom_trans.transform.translation.z = 0.0;
   odom_trans.transform.rotation = odom_quat;

 //send the transform
    odom_broadcaster.sendTransform(odom_trans);

  //next, we'll publish the odometry message over ROS
   nav_msgs::Odometry odom;
    odom.header.stamp = current_time;
   odom.header.frame_id = "odom";

   //set the position
   odom.pose.pose.position.x = x;
   odom.pose.pose.position.y = y;
    odom.pose.pose.position.z = 0.0;
   odom.pose.pose.orientation = odom_quat;

   //set the velocity
   odom.child_frame_id = "base_link";
  odom.twist.twist.linear.x = vx;
  odom.twist.twist.linear.y = vy;
 odom.twist.twist.angular.z = vth;

 //publish the message
   odom_pub.publish(odom);

   last_time = current_time;
    r.sleep();
  }
 }
